High pressure water mist systems work by a combination of heat absorption and oxygen depletion at the heart of the fire and can help to slow the spread of fire by absorbing radiant heat.
This type of system extinguishes fire by distributing amounts of water through nozzles located in the protected area, producing very small droplets at an extremely high speed to achieve maximum cooling effect. The high speed of the droplets means that the mist can penetrate the hot fumes and can reach the combustion area. Water is supplied by either pump units or fixed cylinder systems. This covers systems of just a few nozzles to systems with thousands of nozzles.
Water mist systems are used to provide efficient protection for Class A, B & C fires, though is now used more than ever in data areas due to its economical and ecological reasons. For example, watermist systems do not harm the environment, safe for occupied areas and electrically non conductive (by the use of demineralised water).
For a fire to survive, it relies on the presence of 3 elements; oxygen, heat and combustible material. The removal of any one of these elements will extinguish a fire. High pressure watermist systems attacks two of these elements, heat and oxygen.
The droplets of a water mist system fall more slowly than a conventional sprinkler system. The droplets have a larger surface area and during their discharge from the nozzles, they absorb much more energy. The micro droplets in a high pressure watermist system quickly absorb so much energy that the droplets evaporate and transform from water to steam due to the high surface area relative to the small mass of water. This means that each droplet will expand more than 1700 times, when getting close to the combustible material, whereby oxygen and combustible gases will be displaced from the fire, meaning that the combustible process will increasingly lack oxygen.
Water mist systems with closed nozzles
On standby, the system maintains a pressure within the pipe network of 12 bar. When the temperature exceeds 57°c, the heat sensitive glass bulbs mounted within the protected areas melt. At this point the high pressure pump is automatically activated and the water is dispersed through the nozzles at a pressure of 60-100 bar, thus creating a fire mist only the nozzles with melted bulbs will be activated.
Water mist system with open nozzles
This type of system has dry piping. This system will activate manually or when detectors are set off either by heat, smoke or flame, depending on the type of application. The nozzles are grouped into sections and all the nozzles in the activated section will be released.